(a) Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device provided on one substrate with Schottky barrier diodes having different characteristics.
(b) Description of the Prior Art
It is generally well known that the forward voltage of a Schottky barrier diode is determined by the barrier height, which depends on the impurity concentration of the semiconductor surface and the material of the metal to be in contact with the semiconductor surface.
In order to form plural kinds of Schottky barrier diodes having different forward voltages on one substrate, there already known, for example,
(i) a method of varying the impurity concentration of the substrate surface, for example, by ion implantation and
(ii) a method of changing the metal to be in contact with the substrate surface.
According to the above mentioned method (i), the Schottky barrier diode of a low forward voltage has such problems as the increase of the leakage current, the reduction of the peak inverse voltage and the deterioration of the operating margin at a high temperature.
According to the above mentioned method (ii), the Schottky barrier diode of a low forward voltage is formed by the ohmic contact of such metal as, for example, tantalum (Ta) or a titanium-tungsten (Ti-W) alloy with a silicon substrate surface and has problems that the instability of the substrate surface causes the instability of the characteristics of the Schottky barrier diode and that it is difficult to obtain a desired forward voltage with only the selection of the metal material.